Well head systems for sub sea exploration are traditionally known to comprise a well head having a well head housing secured to a well casing. It also comprises a valve stack, such as a Blow Out Preventer (hereinafter referred to as BOP), located atop a well head during drilling, work-over operations and some phases of the production. Especially, during drilling operations, the drill bit often penetrates pockets of pressurized formations. Due to this, the well bore experiences rapid increase in pressure and unless prevented may result in disastrous blow outs. Hence locating BOPs atop well heads is now very common and indispensable in sub sea exploration.
Now, tubular members such as risers are connected on the top of the well head housing along the through bore of a BOP. The well head housing is in turn secured to the well head casing by welding. When a riser is connected and operated on the top of the well head housing, it creates a very high bending moment on the connecting surface of the lower part of the well head housing and the upper part of the casing, i.e. at the welded joint area. As a result, the well head and casing experiences strain causing substantial fatigue and may eventually initiate cracks on the well head, thereby expediting its deterioration.
In a sub-sea drilling operation the connection of the well head housing and well head casing has to endure stress for 5000 days of the BOP and riser being connected, e.g. during work-over operation and this fairly indicates the amount of strain the well head has to withstand due to bending moment generated during riser operation with a safety factor of 10.
Now to ensure that the well head does not undergo fatigue and tear by bending moment generated during riser operation, it is essential that the BOP should be firmly locked so that less moment is transferred to the weld zone between the well head housing and the casing. This is also essential to ensure that there is no risk of blow out by virtue of a break in the weld between the well head housing and the casing.
Attempts are on over the years to appropriately secure BOPs on well heads to prevent well blow outs, but in prior art technology the approach to ensure firm locking of the BOP on the well head components, with a motive to substantially prevent the effect of bending moment on the lower part of the well head housing and the upper part of the casing during operation of tubular members such as risers, along BOP, is missing.
To be precise, the prior art does not teach locking of a BOP firmly on the well head components, such as the well template, to prevent the well head from movement due to bending moment generated during riser operation, so that fatigue of the well head is substantially reduced during riser operation.
Hence, the issue of withstanding heavy bending moment on the welded area of the housing-casing joint during riser operation and fatigue of the welded joint area still remains unresolved. This consequently, leaves the problem of minimising/nullifying fatigue of the well head and a potential risk for cracks in the joint area, unresolved. The worst eventuality of this can of course be that the well head disconnects from the casing and results in an uncontrollable blow-out.
Accordingly there was a long felt need for a locking technology for locking valve stacks, such as BOPs atop a well head on the well template, so that the effect of bending moment on the well head is substantially reduced.
The present invention meets this long felt need by locking the BOP on beam members of the well template, by providing specially configured locking devices suitably located on axially movable vertical telescopic arms, the arms being positioned along the vertical supporting columns of the BOP.